Radio antenna system



Dec. H, 1931. G R sH I 1,834,274

RADIO ANTENNA SYSTEM Filed May 22, 1928 INVENTOR Gar/90rd E F/fi/mrwz$ ff4 A TTORNE S Patented Dec. ll, 1931 arse stares- PATENT OFFEGE GERHARD B. FISHER, OF PALO ALTO, OALmOB-NIA, ASSIGNOR '10 rnnmar, WERE COMPANY, OF SAN FRANCISCO, CALIFORNIA, A CORPORATION OF CALIFORNIA RADIO ANTENNA cram Application filed May 22,

This invention relates generally to the construction and mode of operation of radio antenna systems, and particularly to antenna systems utilized in radio compass installa- 15 tions.

It is an object of this invention to devise a radia antenna system of the type utilizing a loop antenna associatedwith a nondirectional antenna, which will be constructed in 1Q such a manner that tuning of the loop is substantiall unaffected by adjusting the electrical ba ance between the two branches of the loo 1 t is a further object of this invention to 15 devise a. radio system particularly suitable for the reception of continuous wave signals, the system making ssible a balancing adjustment without su stantially affecting the heterodyne or beat note produced in the refao ceiver.

Further objects of the invention will bea parent from the following description 1n which I have set forth the preferred embodiment of my invention. It is to be understood it that the appended claims are to be accorded a range of equivalents consistent with the state of the prior art.

My system may be outlined briefly as comprisin a loop antenna, in combination with 8b a non irectional antenna, both of which antennae are'associated with a suitable signaling circuit. An electrical balancing device is interposed between the nondirectional antenna and the loop, and means is associated with this balancing device whereby it may be adjusted at will without aflecting tuning of the loop. The signaling device is preferably of the heterodyne type, as the system is particularly valuable for receiving continuous wave signals. However certain features of my invention are believed broadly new as applied to signaling systems in general.

In the drawing I have. illustrated my systern as comprising a loop antenna 10, which if the system is to be utilized for taking radio compass observations, is mounted so as to be rotatable about a vertical axis. Associated with this loop antenna there is a suitable signaling circuit 11, principally of the vacuum tube type, as will be presently described.

1928. Serial No. 279,638.

Tuning of the loop is effected by means of an associated variab e reactive element as for example a variable condenser 12. Cbupling between the loop antenna and the signalin circuit 11 is efi'ected preferably by means 0% an electrically symmetrical arrangement such as is provided by a pair of series connected coils 13, these coils being included in the terminals of the antenna 10 and having variable condenser 12 interposed between the same. Coils 13 are conjointly inductively coupled with coil 14 which is included in the input circuit of signalin circuit 11.

As is customary in ra 'o compass installations, I prefer to divide the antenna 10 into two electrical branches. This may be effected by connecting the midpoint of loop 10 to a pointof neutral tential, such as the ground connection 16. t is commonly known that a loop antenna receives si als of maximum intensity along the direction of the plane of the loop, and that signals will be practically of zero intensity when received alon a direction at right angles to the plane 0 the loop. The characteristic curve of such a loop I) itself approximates a figure 8, in other wor it is bilaterally directional. In actual practice however the theoretical figure 8 characteristic is modified to such an extent asto render such a system inaccurate fora-direction finders or radio compasses, due principally to the influence of ground currents.

arious electrical means have been employed for securing a erfect balance between the two branches of a oop antenna, thus making possible a closer approximation to the theoretical figure 8 characteristic. In the past such balancing 'devices have been associated with a loop antenna in such a way as to have a certain effect upon the tuning of the loop. When the system is being employed for comparatively long wave length signals, a slight variation in the tuning of the loop will not affect the reception, but such a variation becomes noticeable and is a distinct detriment when the system is being employed for relatively short wave lengths. Furthermore when receiving .signals by the heterodyne method, that is when beating the incoming signals with a local diiferent frequency-in order to produce a differential tone freuency, a change in the ?tuning of the loop us to adjustments of the balancing device is sufficient to cause a variation in the beat frequency and such is objectionable and may be confusing to an observer. As has been reviously mentioned, in my invention the Balancing device is associated with the loop antenna in 'such a way as to have substantially no effect upon the tuning of the loop.

Referring a ain to the drawing, I have shown a non irectional antenna 15 connected to an electrical balancing device 17. I prefer to employ a capacitative balancing device consisting of a central condenser electrode 18 connected to antenna 15 and movable with respect to electrodes 19 and 20. With such a device the respective capacitances afforded by electrodes 19 and 20' with respect to electrode 18, may be varied simultaneously and oppositely by shifting electrode 18. While prefer to employ a capacitative balancin device, it is understood that inductive or ot er reactive balancing devices may be emplo ed which utilize two reactive elements capab e of opposite and simultaneous variation.

For associating the balancin device 17 with the loop antenna circuit, I ave shown a pair of series connected coils 21 connected across electrodes 19 and 20, and both mutual- 1yl inductively coupled with another coil 22, t is latter coil being inserted in series with one of the branches of the loop 10. Coils 21 preferably have the connection between the same connected to a point of neutral potential and for convenience I make both coils 21 of a single continuous windin having its midpoint tapped for the groun connection 23. Coils 21 together with balancing device 17 form a circuit antiresonant to the signals to be received.

In order that the signaling circuit 11 may receive continuous wave signals by the heterodyne method, I have shown an electron relay 26 which is adagted to oscillate at a frequency somewhat di erent from the incoming signal frequency. Such an arrangement can be afforded by an ordinary oscillating audion relay such as shown. For example I have shown the inductance 14 as being included inithe in ut or grid circuit of electron relay 26, an this inductance is tuned as by means of variable condenser 27 Coil 14 is preferably divided into two electrical sections by ground connection 25. The output or plate circuit of the relay, which is supplied with a suitable source of direct current as by means of the battery 28, also includes an inductance 29 coupled with inductance 14 so as to secure feed back of energy from the output into the input circuit of electron relay 26. The amount of energy fed back may be conveniently controlled as by means of variable condenser 31 inserted in series with eeann coil 29. A choke 82 has been shown in series with B battery 28, in order to prevent bypassing of radio frequency currents.

As is well known such a receiving circuit as described above can be adjusted so as to oscillate locally at a frequency differing from the radio frequency of s1 als being received. The beat frequency so ormed or any other resultant frequency ma be detected and then translated or may be urther amplified, detected and then translated. For simplicity I have shown the output of relay 26 as being device 33 which sup- 7 coupled to a detectin plies a suitable translator 34. n this particular instance the beat frequency is made of an audible tone frequency so as to produce an audible response in the translator 34, this translator bemg usually the ordinary tel iiplhone receivers.

0 operation of'my system is as follows: The loop antenna is tuned as by means of a variable condenser 12, to the frequency of signals to be received. The signaling circuit 11 is also adjusted so as to receive such signals. If a proper electrical balance does not exist between two branches of 100 10 the characteristics of the system will not a true figure 8. By adjusting the balancing device 17 however the operator can vary the proportionate amount of energy flowing in the coils 21, and thus the character of the currents induced in coil 22 can be varied. For a certain position of electrode 18 of the balancin device, an exchange of energy will be eifecte between the two antenna to balance out disturbing ground currents in the loop antenna. Thus Eerfect symmetry between the two loop branc es can be secured and the system can to an Ewart cnam because with this link in a directional characteristic.

Since coils 21 have a fixed relationship with respect to coils 22, it is apparent that adjustment of the balancing device has practically no effect upon tuning of the loop circuit. Thus as far as tuning of the loop is concerned, the balancing device is electrically isolated from the loop antenna. As has been previously explained this result is to be desired, since an operator may then make any necessar adjustments of the balancing device wit out affecting reception of signals. When the receiving system is arranged for heterodyne reception, as shown and described, there will be practically no variation of the beat frequency as the balancing device 17 is ad- 'usted.

By shifting electrode 18 sufliciently close to one of electrodes 19 and 20, and by employing phase shifting means, the system can be given the characteristics of a cardiod, in which event balancing device 17 can be adjusted to make the cardiod characteristic more erfect. Phase shifting means can be provi ed by a resistance 36 inserted in the lead from antenna and normally shunted by a switch 37.

My system is particularly useful as a direction finder or radio compass operating on 5 short waves as it makes possible convenient ad ustment of the balancing device to secure a sharp minimum response, without makin a compensating adjustment of the tuning o the loop.

1. In a radio s stem, a directional antenna, a non-directiona antenna, a signaling circuit cooperably associated with said antennae, a pair of series connected reactive elements conjointly serving to cou le said antennae, the connection between said elements being connected to a point of neutral potential, a reactive balancin device included in a cir-, cuit together wit said elements and connected with said non-directional antenna, the arrangement of said elements and said balancing device being such as to render tuning of the directional antenna immune from a ustments of said balancing device.

2. In a radio receiving system, a loop antenna, a non-directional antenna, a signaling circuit coupled to said 100 ,means for tunin said loop, a coil connecte in series with sai loop, a pair of series connected .coils both coupled to said first coil, the connection between said latter coils being connected to a int of neutral potential, and a reactive ha ancing device having connection with said nondirec tional antenna and connected in a circuit which includes said pair of coils.

3. In a directional radio system, a tunable circuit comprising a loop, a connection from earth to su stantlally t e midpoint of said loop, an open antenna system, a transformer having a differential rima and a secondary winding dispose in said antenna system and tunable circuit respectively, means to vary the relative magnitu es of current in said primary winding, a signalling circuit, a transformer having primary and secondary windin disposed respectively in said tunable an signalling circuits, and a connection from earth to substantially the midpoint of said secondary.

In testimony whereof, I have hereunto set my hand.

FISHER. 

